The present invention is directed to the field of percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) procedures generally, and more particularly, to a device and method which allow an interventional medical device, such as a stent-delivery catheter, to traverse an arterial lesion without dislodging friable arterial plaque during delivery of the interventional device through the lesion.
In a typical balloon angioplasty procedure, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries by means of a conventional Seldinger technique and advanced within a patient""s vascular system until the distal end of the guiding catheter is positioned at a point proximal to the lesion site. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient""s vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the lesion. Once in position, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter may be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
Angioplasty procedures, by necessity, stretch and tear the tissue of the artery wall in the region of treatment with a resultant reduction in strength. As a consequence, radial collapse of the vessel lumen occurs in a certain percentage of cases. In order to prevent radial collapse of a dilated vessel, a physician can implant an intravascular prosthesis for maintaining vascular patency across the dilated region. Such prostheses are small tubular metallic structures commonly referred to as stents. The stent is crimped tightly onto the balloon portion of a dilatation catheter and is advanced through the guiding catheter already in place in the patient""s vasculature. The stent is positioned so that it bridges the dilated region when expanded by an expandable member, such as balloon, and is thus implanted in the artery.
In lightly occluded arteries, some physicians prefer to expand the artery and implant a stent in a single operation. However, in heavily occluded arteries, this procedure has proven somewhat dangerous as the metallic structure of the stent tends to dislodge the arterial plaque thereby forming emboli which will be released into the patient""s bloodstream. Such emboli may become lodged in a small diameter blood vessel and can occlude or partially occlude the vessel. When angioplasty is performed in the carotid arteries, the risks associated with emboli are particularly high since emboli which may be produced present a significant risk of ischemic stroke should a blood vessel leading to the brain become occluded.
Therefore, in heavily occluded vessels, the presently preferred procedure is to first dilate the artery across the lesion site and withdraw the dilatation catheter. This step is commonly referred to as pre-dilatation. In a second step, a stent is expanded and implanted across the previously dilated lesion site usually by means of a second delivery catheter. This two-step procedure is advantageous since the stent is less likely to dislodge arterial plaque in the pre-dilated artery and therefore the risk posed by emboli is somewhat reduced. However, the two-step procedure has some disadvantages in that the artery wall undergoes additional trauma during the second dilatation procedure and may suffer additional loss of strength.
The majority of devices that have been proposed as solutions to the problem of emboli generated during an angioplasty procedure may be categorized as intravascular filters that attempt to capture or trap emboli flowing within the patient""s blood stream. There are many examples of such filters, one of which is described in U.S. Pat. No. 5,152,777, entitled xe2x80x9cDevice and Method for Providing Protection From Emboli and Preventing Occlusion of Blood Vesselsxe2x80x9d issued to Goldberg et al. This device consists of a filter having of a plurality of resilient, stainless steel wire arms joined at one end so as to form a conical surface, and having rounded tips at their other ends to prevent damage to the vessel walls. This filter is intended to be removable and is designed to be deployed from either a small diameter catheter or a hollow guidewire.
Another example of an intravascular filter is described in U.S. Pat. No. 4,873,978, entitled xe2x80x9cDevice and Method for Emboli Retrievalxe2x80x9d issued to Ginsburg. Ginsburg discloses a removable vascular filter permanently attached to a wire for deployment from a catheter. The filter is comprised of a bundle of longitudinal wires secured together at the point of attachment to the deployment wire. Interconnecting each adjacent longitudinal wire is a transverse wire which forms a zig-zag pattern. The filter is introduced through a catheter. Upon deployment, the filter wires expand to form a wire mesh, thereby obstructing the vessel and straining the blood flowing there through.
One drawback of many prior art filtering devices is the relatively large size of the wire mesh or straining elements used in the filters. Large mesh filters may allow for adequate blood flow but sometimes fail to trap all of the small emboli. Fine mesh filters may not provide an adequate solution to this problem as they generally have a low percolation rate which may tend to limit blood flow within the vessel and may induce blood depravation downstream from the area of deployment. In addition, the various prior art devices do nothing to alleviate the need for pre-dilatation of heavily occluded arteries prior to stent placement.
Given these and other limitations of the prior art filters, it becomes apparent that there is a need for an alternative device or method that would reduce the likelihood of emboli formation during an interventional procedure and would therefore increase the efficacy of existing intravascular filters. Ideally, such a device would also allow a stent delivery catheter to be introduced into a highly occluded artery without the necessity of pre-dilatation and would therefore reduce trauma imposed on an artery wall. Further, such a device should be compatible with existing catheters and other equipment used in angioplasty procedures. The present invention satisfies these and other needs.
The present invention provides an elastically and/or geometrically expandable, low friction, low profile delivery sheath attached to the distal end of a catheter. The delivery sheath serves to form a protective barrier between arterial lesions composed of friable arterial plaque and an interventional device, such as a stent delivery catheter, subsequently introduced through the sheath to treat the lesion. In use, the expandable delivery sheath is introduced into a guiding catheter which has been previously placed at a location proximal to the lesion site. The expandable sheath is advanced through the guiding catheter and deployed such that it traverses the arterial lesion. Due to its low profile and elastic nature, the delivery sheath should not dislodge arterial plaque in a highly occluded artery. A stent delivery catheter then can be introduced into the expandable sheath. The expandable sheath, which is designed to have a diameter smaller than that of the stent delivery catheter, expands upon introduction of the stent delivery catheter to form a glove-like fit over the stent and its delivery catheter. Due to the sheath""s low coefficient of friction, the stent delivery catheter may be easily advanced through the sheath until the stent bridges the lesion within an artery. As the stent and its delivery catheter traverse the lesion, the sheath forms a protective barrier between the stent and the friable arterial plaque of the lesion to help prevent the formation of emboli that would otherwise be created by abrasive forces if the stent crossed the lesion without the presence of such a delivery sheath.
The delivery of the stent delivery catheter also causes the lesion to compress somewhat to conform to the larger diameter of the stent delivery catheter. In this manner, the advancement of the stent delivery catheter across the lesion provides some pre-dilatation of the stenosis. Prior to expansion of the stent, the delivery sheath, having served its purpose, can be withdrawn from the area of treatment back into the guiding catheter. Thereafter, the stent can be expanded fully in the artery to compress the lesion and restore adequate blood flow through the area of treatment.
The present invention reduces the likelihood of emboli formation by providing a low profile sheath that may easily cross a lesion without abrading the lesion. Once in place, the delivery sheath forms a protective barrier between the lesion and any subsequently introduced interventional device. Thus, the expandable sheath of the present invention increases the safety and efficacy when performing interventional procedures. In addition, the present invention may reduce the need for pre-dilatation of a lesion prior to placement of the stent to thereby minimize trauma to the artery wall.
These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings.